Immunocytochemical analysis of a monoclonal antibody specific for rainbow trout (Oncorhynchus mykiss) granulocytes and thrombocytes

A monoclonal antibody against rainbow trout peripheral blood leucocytes was selected for its lack of reactivity with rainbow trout immunoglobulin. Its reactivity with leucocytes from peripheral blood, head kidney and spleen was analysed by flow cytometry and electron microscopy, and compared with that of monoclonal antibodies directed against rainbow trout immunoglobulin, which reacted with B cells, B lymphoblasts and plasma cells. The antibody reacted with 5–20% of the peripheral blood leucocytes, 8–9% of head kidney leucocytes and 5–7% of spleen leucocytes. Electron microscopical immunocytochemistry revealed that the antibody reacted strongly with granulocytes and weakly with thrombocytes, and not with erythrocytes, lymphocytes, monocytes or macrophages. The antibody has possible applications in the identification and isolation of rainbow trout leucocytes, either alone or in combination with other monoclonal antibodies.